All questions of Origin of Soil & Soil-Water Relationship for Civil Engineering (CE) Exam

C, go for some notes, most USED method is oven dry

Answer:
A well-graded soil has a coefficient of curvature between 1 to 3. This means that the soil particles in a well-graded soil are distributed over a wide range of sizes, which helps to improve the overall stability and engineering properties of the soil.

Coefficient of Curvature:
The coefficient of curvature (Cc) is a measure of the uniformity of the particle size distribution in a soil sample. It is calculated using the formula:
Cc = (D30)^2 / (D10 x D60)
where D10, D30, and D60 are the particle sizes corresponding to 10%, 30%, and 60% passing, respectively, in a grain size distribution curve.

Explanation of Options:

a) 10 to 12: This range of coefficient of curvature indicates a poorly graded soil, where the soil particles are mainly concentrated in a narrow range of sizes. This can result in reduced stability and engineering properties of the soil.

b) 7 to 9: Similar to option (a), this range also indicates a poorly graded soil with a narrower particle size distribution. This can lead to problems such as erosion and reduced load-bearing capacity.

c) 4 to 6: This range of coefficient of curvature indicates a gap-graded soil, where there is a significant gap or discontinuity in the particle size distribution. This can result in uneven settling and poor compaction characteristics.

d) 1 to 3: This is the correct range for a well-graded soil. A well-graded soil contains a wide range of particle sizes, which helps to achieve better compaction, drainage, and load-bearing capacity. The presence of various particle sizes allows for better interlocking and reduces the chances of particle segregation.

Importance of Well-Graded Soil:

1. Improved Compaction: The presence of a wide range of particle sizes in a well-graded soil helps to achieve better compaction and reduce settlement.

2. Better Drainage: Well-graded soils have improved permeability due to the presence of larger particles, allowing for efficient drainage of water.

3. Increased Stability: The interlocking of different particle sizes in a well-graded soil enhances its stability and resistance to erosion.

4. Enhanced Load-Bearing Capacity: The presence of different particle sizes in a well-graded soil helps to distribute loads more evenly, resulting in increased load-bearing capacity.

In conclusion, a well-graded soil has a coefficient of curvature between 1 to 3. This range indicates that the soil particles are distributed over a wide range of sizes, leading to improved stability, compaction, drainage, and load-bearing capacity.

Viscosity of water/liquid is expressed in KN-s/m2. Let's break down the answer into headings and bullet points for better understanding:

Viscosity:
Viscosity is defined as the measure of a fluid's resistance to flow. It is a property of the fluid, and it varies with temperature, pressure, and composition.

Units of Viscosity:
Viscosity is expressed in different units depending upon the system of units used. The SI unit of viscosity is Pascal-second (Pa·s). Other commonly used units are:

- Poise (P) or centipoise (cP)
- Stokes (St)
- Reynolds (Re)
- Saybolt Universal Seconds (SUS)

However, in civil engineering, viscosity is often expressed in kilonewton-seconds per square meter (KN-s/m2). This unit is equivalent to Pa·s, which is the SI unit of viscosity.

Importance of Viscosity:
Viscosity plays a crucial role in various fields of engineering, such as:

- In civil engineering, viscosity is important in the design of hydraulic structures, such as dams, canals, and culverts.
- In chemical engineering, viscosity is essential in the design of pipelines, pumps, and heat exchangers.
- In mechanical engineering, viscosity is significant in the design of lubrication systems, such as engines, gears, and bearings.

Conclusion:
Viscosity is an essential property of fluids, and it is expressed in different units depending upon the system of units used. In civil engineering, viscosity is often expressed in KN-s/m2, which is equivalent to Pa·s, the SI unit of viscosity. Understanding viscosity is crucial in various fields of engineering, as it affects the design and performance of different systems.

**Liquid Limit of Soils**

The liquid limit is a property of soils that represents the moisture content at which the soil transitions from a plastic state to a liquid state. It is an important parameter in geotechnical engineering as it helps determine the soil's behavior and shear strength.

**Shear Strength of Soils**

Shear strength is the resistance of a soil to shearing forces. It is a crucial factor in determining the stability of slopes, retaining walls, and foundations. Shear strength of soils is influenced by various factors including the soil type, density, moisture content, and stress conditions.

**Explanation of Answer**

The correct answer to the given question is option 'A': Same shear strength of small magnitude. This means that at the liquid limit, all soils possess the same shear strength, but it is of relatively small magnitude.

This answer is based on the behavior of soils at the liquid limit. When a soil reaches its liquid limit, it becomes highly saturated with water and loses its ability to resist shear stresses effectively. At this moisture content, the soil particles are suspended in water, causing a decrease in the soil's cohesion and shear strength.

**Reasoning behind Option A**

The reason why all soils possess the same shear strength at the liquid limit is primarily due to the loss of cohesion. Cohesion is the component of shear strength that arises from interparticle attractive forces in cohesive soils. These attractive forces are mainly due to the bonds between particles, such as clay minerals.

When a soil is in a plastic state, it can resist shearing forces to some extent due to cohesion. However, as the moisture content increases and the soil transitions to the liquid state at the liquid limit, the cohesive forces between particles are greatly reduced. This reduction in cohesion results in a decrease in shear strength.

**Magnitude of Shear Strength**

The shear strength at the liquid limit is of relatively small magnitude compared to the shear strength of soils in a consolidated or semi-solid state. This is because the soil is in a highly saturated and loose state at the liquid limit, which leads to a lower resistance to shearing forces.

In contrast, soils in a consolidated or semi-solid state, such as those with lower moisture contents, have higher shear strengths. The particles in these soils are more closely packed, leading to increased frictional forces and interparticle bonding, which contribute to higher shear strength.

**Conclusion**

In summary, at the liquid limit, all soils possess the same shear strength of small magnitude due to the loss of cohesion. This is because the soil is in a highly saturated and loose state, leading to a decrease in shear strength compared to soils in a more consolidated or semi-solid state. Understanding the behavior of soils at different moisture contents is essential for geotechnical engineers to design safe and stable structures.

The main disadvantage of seive analysis method is that it require much more time , labour and also tedious method . So I think Time consuming is the best option for this question .( A )

The correct answer is option 'D', Aeolian soil. Aeolian soil refers to the soil that is formed by the transportation of weathered rock material by the wind. This type of soil is commonly found in arid and semi-arid regions where there is a lack of vegetation cover, and the wind is the dominant geological agent of erosion and transportation.

Here is a detailed explanation of why aeolian soil is formed by wind transportation:

Formation of Aeolian Soil:
1. Weathering: The process of weathering breaks down rocks into smaller particles over time. This can be caused by physical, chemical, or biological processes.
2. Erosion: In arid and semi-arid regions, where there is limited vegetation and sparse rainfall, wind erosion becomes the primary agent of erosion. The wind picks up the weathered rock particles and transports them over long distances.
3. Transportation: The wind carries these particles, ranging in size from silt to sand, and transports them through the air. This process is known as suspension.
4. Deposition: When the wind loses its energy, it drops the transported particles, leading to their deposition. This deposition occurs in areas where the wind velocity decreases, such as behind obstacles like dunes, slopes, or vegetation.
5. Soil Formation: Over time, the deposited particles accumulate, mix with organic matter, and undergo various processes like weathering, leaching, and microbial activity. These processes contribute to the formation of soil.

Characteristics of Aeolian Soil:
1. Texture: Aeolian soil is characterized by its texture, which is predominantly sandy or silty. The particles are usually well-sorted, meaning they are similar in size, due to the wind's selective transportation of particles based on their weight.
2. Porosity and Permeability: Due to the sandy nature of aeolian soil, it generally has high porosity and permeability, allowing water to drain quickly.
3. Lack of Organic Matter: Aeolian soil is often deficient in organic matter due to the arid and semi-arid conditions in which it is formed. This lack of organic matter affects its fertility and nutrient content.
4. Presence of Wind-Formed Features: Aeolian soil is often associated with various wind-formed landforms such as sand dunes, loess deposits, and desert pavements.

In conclusion, aeolian soil is formed by the transportation of weathered rock material by the wind. This process involves the erosion, transportation, and deposition of particles, resulting in the accumulation and subsequent formation of soil in arid and semi-arid regions.

Explanation:

Flat portion in particle size distribution curve indicates intermediate size particles are missing
- A curve with a flat portion in a particle size distribution curve indicates that there is a range of particle sizes that are not present in the sample being analyzed.
- This flat portion suggests that there is a lack of particles of intermediate size in the sample.
- The absence of intermediate size particles can impact the overall characteristics and properties of the material being analyzed.
- It is important to understand the particle size distribution of a material as it can greatly influence various properties such as strength, permeability, and reactivity.
Therefore, in the context of a particle size distribution curve, a flat portion indicates that intermediate size particles are missing from the sample.

Explanation:

The water content of a soil sample is a measure of the amount of water present in the soil sample. It is an important parameter in geotechnical engineering as it affects the engineering properties of soil, such as its strength, compressibility, and permeability.

There are several methods available to determine the water content of a soil sample, but one method that cannot be used is the pipette method.

Reason:
The pipette method is commonly used to determine the particle size distribution of fine-grained soils, such as silt and clay. It involves using a pipette to extract a small amount of soil suspension from a water sample and then analyzing the sedimentation of particles to determine the particle sizes present in the soil sample. However, this method does not provide a direct measure of the water content of the soil sample.

Other Methods:
There are several other methods available to determine the water content of a soil sample, including:

1. Oven drying: This method involves weighing a soil sample, drying it in an oven at a specified temperature, and then reweighing the dried sample to determine the water content. The difference in weight before and after drying represents the water content.

2. Alcohol: The alcohol method involves mixing a soil sample with a measured amount of alcohol, which displaces the water in the soil. The mixture is then heated to evaporate the alcohol, and the difference in weight before and after heating is used to calculate the water content.

3. Calcium carbide: This method involves adding a known amount of calcium carbide to a soil sample and sealing it in a container. The calcium carbide reacts with the water in the soil, producing acetylene gas. The pressure of the gas is measured, and from this, the water content of the soil sample can be calculated.

In conclusion, the water content of a soil sample cannot be determined by the pipette method. This method is used for particle size analysis and does not provide a direct measure of the water content. Other methods, such as oven drying, alcohol, and calcium carbide, are commonly used to determine the water content of soil samples.

Particle Size Distribution Curve:

The particle size distribution curve is a graphical representation of the proportion of different sizes of particles in a soil sample. It is plotted with the percentage of soil particles smaller than a particular size on the y-axis and the particle size on the x-axis. The curve provides valuable information about the soil's gradation, which is important for engineering purposes.

Interpretation of the Curve:

The curve is typically divided into three regions: fine-grained soil, coarse-grained soil, and gravel. The right side of the curve represents the larger particle sizes, while the left side represents the smaller particle sizes.

Coarse-Grained Soil:

Coarse-grained soil refers to soils with a significant proportion of larger-sized particles, such as sand and gravel. These particles are generally visible to the naked eye and can be felt when rubbed between the fingers. Coarse-grained soils have relatively higher permeability and lower plasticity compared to fine-grained soils.

Right Side of the Curve:

The right side of the particle size distribution curve represents the larger particle sizes. This portion of the curve indicates the proportion of coarse-grained soil in the sample. As the particle size increases from left to right, the percentage of soil particles smaller than that size decreases.

Conclusion:

Therefore, the curve situated at the right side of the particle size distribution curve represents coarse-grained soil. This means that the soil sample has a significant proportion of larger-sized particles, which are characteristic of coarse-grained soils like sand and gravel.

Soil Classification based on Plasticity Index

The plasticity index (PI) of a soil is a measure of its plasticity or ability to undergo deformation without cracking. It is calculated by subtracting the plastic limit (PL) from the liquid limit (LL) of the soil. The plasticity index is an important parameter used in soil classification systems to categorize soils into different groups.

The Indian Standard (IS) classification system is commonly used in India to classify soils based on their properties. According to this system, the soil is represented by letter symbols based on its classification.

Given that the fine-grained soil has a liquid limit of 60 and a plastic limit of 20, we can calculate the plasticity index as follows:

PI = LL - PL
= 60 - 20
= 40

The plasticity index of the soil is 40.

Soil Classification Based on Plasticity Index

To determine the soil classification based on the plasticity index, we refer to the plasticity chart provided by the Indian Standard classification system.

The plasticity chart consists of different zones representing different soil types based on their plasticity index values. These zones are labeled with letter symbols.

In this case, since the plasticity index is 40, we need to locate this value on the plasticity chart to determine the corresponding soil classification.

According to the plasticity chart, a soil with a plasticity index of 40 falls within the CH zone.

Soil Classification Result

Therefore, based on the plasticity index of 40, the soil is represented by the letter symbol "CH" according to the IS classification system.

Conclusion

In conclusion, when a fine-grained soil has a liquid limit of 60 and a plastic limit of 20, the soil is represented by the letter symbol "CH" as per the Indian Standard (IS) classification system. The CH symbol indicates that the soil is a clay of high plasticity.

Answer:

The Soviet liquid limit device, also known as the Casagrande method, is a tool used in geotechnical engineering to determine the liquid limit of soil. The liquid limit of a soil is the moisture content at which the soil transitions from a plastic state to a liquid state. In other words, it is the moisture content at which the soil begins to flow under its own weight.

Principle of Station Penetration:
The Soviet liquid limit device is based on the principle of station penetration. This principle involves measuring the resistance of a soil sample to penetration as its moisture content is gradually increased. The device consists of a brass cup with a flat-bottomed groove, a crank mechanism, and a counter.

Procedure:
The procedure for determining the liquid limit using the Soviet liquid limit device involves the following steps:

1. A small soil sample is taken and mixed with water to form a paste-like consistency.
2. The soil paste is placed in the brass cup and leveled off.
3. The device is operated by rotating the crank at a constant speed, causing a plunger to penetrate the soil sample.
4. The number of revolutions required for the groove to close over a distance of 1 cm is recorded.
5. The moisture content of the soil sample is then calculated based on the number of revolutions.

Interpretation:
The liquid limit of the soil is determined by conducting multiple tests at different moisture contents. The moisture content at which the groove of the soil sample closes over a distance of 1 cm in 25 blows is considered the liquid limit.

The principle of station penetration allows for the measurement of the soil's resistance to penetration as its moisture content changes. This resistance is influenced by the cohesive forces between soil particles, which increase as the moisture content decreases. Therefore, the greater the number of revolutions required to close the groove, the higher the liquid limit of the soil.

Advantages of the Soviet Liquid Limit Device:
- Simple and easy to operate
- Provides reliable and accurate results when performed correctly
- Can be used for a wide range of soil types

Limitations:
- The device requires a skilled operator to ensure consistent and accurate measurements.
- Results may be affected by factors such as sample preparation, temperature, and operator technique.
- The device does not account for soil characteristics such as particle size distribution and plasticity index, which can also influence the liquid limit.

Calcium Carbide Method Overview
The calcium carbide method is primarily used for the production of acetylene gas, which has significant applications in various industries, especially in welding and cutting.
Production Process
- Calcium carbide (CaC2) is produced by heating limestone (CaCO3) and carbon (C) in an electric arc furnace.
- When calcium carbide reacts with water, it generates acetylene gas (C2H2) and calcium hydroxide (Ca(OH)2) as a byproduct.
Chemical Reaction
- The reaction can be summarized as follows:
- CaC2 + 2H2O → C2H2 + Ca(OH)2
Significance of Acetylene
- Acetylene is a colorless gas that is highly flammable and has a garlic-like odor.
- It is widely used as a fuel in oxy-acetylene welding, cutting metals, and in the synthesis of various organic compounds.
Why Other Options Are Incorrect
- a) Methane: Methane (CH4) is a different hydrocarbon and is primarily produced through natural gas extraction or biological processes.
- b) Carbon Dioxide: While carbon dioxide (CO2) can be a byproduct in some reactions, it is not the main product of the calcium carbide method.
- d) Oxygen: Oxygen (O2) is not produced in this reaction; in fact, it is consumed in combustion processes involving acetylene.
Conclusion
In conclusion, the primary gas produced during the calcium carbide method is acetylene (option C), making it essential for various industrial applications.

In the given formula, the variable "f" is equal to 105.

Understanding Wet Soil Volume in Shrinkage Dish
The volume of wet soil in a shrinkage dish is a critical aspect in soil mechanics and civil engineering. The shrinkage dish test evaluates the water content and shrinkage behavior of soil, which helps in understanding its compaction and stability characteristics.
Key Concepts
- Shrinkage Dish: This is a shallow dish used to measure the volume of soil. It allows for a controlled environment where the soil can dry and shrink.
- Wet Soil Volume: The volume of wet soil refers to the space occupied by the soil when it is saturated with moisture.
Reason for One-Third Volume
- Soil Behavior: When wet, soil particles are held together by water, affecting its physical properties. The volume of wet soil is typically one-third of the total volume of the dish. This correlation arises from the soil's inherent structure and how it interacts with water.
- Testing Standards: According to testing standards in soil mechanics, particularly when assessing plasticity and moisture content, the expected volume of wet soil in a shrinkage dish is standardized to be one-third of the total volume of the dish.
Conclusion
Understanding the volume of wet soil in a shrinkage dish is essential for civil engineers. This standardized measurement aids in predicting how soils will behave under various moisture conditions, which is crucial for effective design and construction practices. Hence, the correct answer indicating that the volume of wet soil in the shrinkage dish is one-third of the volume of the dish is option 'C'.

B) VS = (VD-VL)/VD

Given data:
Diameter of particle, d = 0.06 cm
Height of settling, H = 10 cm

We can use Stoke's law to find the time for settling of particle.

Stoke's law relates the settling velocity of a particle to its diameter and density of fluid as follows:
V = (2/9) * (ρp - ρf) * g * (d/2)^2 / η
where,
V = settling velocity of particle
ρp = density of particle
ρf = density of fluid
g = acceleration due to gravity
d = diameter of particle
η = viscosity of fluid

We can assume the density of particle to be 2650 kg/m^3 (for a typical mineral particle) and density of fluid (water) to be 1000 kg/m^3. The viscosity of water at 20°C is 1.002 x 10^-3 Pa.s.

Converting the given data to SI units, we have:
d = 0.0006 m
H = 0.1 m
ρp = 2650 kg/m^3
ρf = 1000 kg/m^3
g = 9.81 m/s^2
η = 1.002 x 10^-3 Pa.s

Substituting these values in Stoke's law equation, we get:
V = (2/9) * (2650 - 1000) * 9.81 * (0.0006/2)^2 / (1.002 x 10^-3)
V = 8.81 x 10^-6 m/s

The time taken for settling of particle can be found as:
t = H / V
t = 0.1 / 8.81 x 10^-6
t = 25.8 s

Therefore, the correct answer is option A) 25.8 s.

The Relation for Calculating Plastic Index

The plastic index (IP) is a term used in geotechnical engineering to measure the plasticity of fine-grained soils. It is an important parameter for determining the engineering properties and behavior of soils, especially in the field of soil mechanics. The plastic index is calculated using the relation:

IP = WL - WP

Where:
- IP represents the plastic index
- WL is the liquid limit of the soil
- WP is the plastic limit of the soil

Let's break down the components and explain each of them in detail.

Liquid Limit (WL)
The liquid limit is a measure of the moisture content at which a soil transitions from a plastic state to a liquid state under specific testing conditions. It is determined using the Casagrande method or the fall cone method. During the test, the soil sample is repeatedly sheared until it flows like a liquid. The moisture content at this point is recorded as the liquid limit.

Plastic Limit (WP)
The plastic limit is the moisture content at which a soil transitions from a semi-solid plastic state to a brittle solid state. It represents the minimum moisture content at which the soil can still be molded and retain its shape. The plastic limit is determined using the thread-rolling method or the plastic limit test. In this test, a soil sample is rolled into a thread until it crumbles or breaks apart. The moisture content at this point is recorded as the plastic limit.

Plastic Index (IP)
The plastic index is a numerical value that indicates the range of moisture content within which the soil exhibits plastic behavior. It represents the difference between the liquid limit and the plastic limit of the soil. The plastic index provides information about the soil's compressibility, expansiveness, and potential for volume change.

By subtracting the plastic limit (WP) from the liquid limit (WL), the plastic index (IP) is obtained. A higher value of the plastic index indicates a greater plasticity of the soil, whereas a lower value indicates less plasticity. Soils with high plasticity are typically clayey soils, while soils with low plasticity are usually sandy or gravelly soils.

In conclusion, the plastic index is calculated by subtracting the plastic limit from the liquid limit of a soil. This calculation provides valuable information about the soil's behavior and engineering properties, helping engineers and geotechnical professionals in designing and analyzing structures built on or with soils.

Tools for Grooving Sandy Soil

The type of tool that is preferred for grooving sandy soil is the ASTM tool. This tool is commonly used in geotechnical engineering to determine the density and moisture content of soil. It consists of a cylindrical metal mold with a detachable collar and a metal rammer.

ASTM Tool

The ASTM tool is designed to be used on cohesive soils, but it can also be used on sandy soils. It is a simple and effective tool for determining the in-situ density and moisture content of soil. The tool is inserted into the soil and the collar is removed. The soil is then compacted using the rammer and the collar is replaced. The soil is then excavated from the mold and the density and moisture content are determined.

Advantages of ASTM Tool

Some of the advantages of using the ASTM tool for grooving sandy soil include:

1. Simple and easy to use
2. Provides accurate and reliable results
3. Can be used on a variety of soil types
4. Portable and lightweight

Conclusion

In conclusion, the ASTM tool is the preferred tool for grooving sandy soil. It is a simple and effective tool for determining the in-situ density and moisture content of soil. It is important to use the correct tool for the soil type to ensure accurate and reliable results.